Devices using various types of disks, such as optical disks, optomagnetic disks, flexible magnetic disks, etc., are known as disk drives. Of these, a hard disk drive (HDD), which is a magnetic disk drive, is used in many electronic devices, such as video recording and playback devices, car navigation systems, personal music devices, in addition to computer systems.
A magnetic disk used in an HDD has a plurality of data tracks and a plurality of servo tracks formed in concentric circular shapes. Each servo track is comprised of a plurality servo sectors containing address information. in addition, each data track is comprised of a plurality of data sectors which may include user data. The data sectors are recorded between the servo sectors, which are separated in the circumferential direction. A head element of a head slider supported by an oscillating actuator can write data to the data sectors and read out data from the data sectors by accessing the desired data sector in accordance with the address information in the servo sectors.
An HDD repeatedly writes and reads data on the recording surface of a magnetic disk. As a result of higher density magnetic recording in the past few years, the leakage magnetic field from the head slider during a data write to the selected data track is known to affect the magnetic data in the adjacent tracks. In addition, repeated magnetization changes in a data track are known to affect the magnetization of the adjacent data tracks. Therefore, when data are repeatedly written to a data track, the interference with the adjacent data tracks occurs repeatedly due to the leakage of the magnetic field from the head slider and the magnetization changes of the data track, which causes the data in the adjacent data tracks to change, and data losses (read hard errors) may occur.
To prevent this type of read hard error, a proposal in Japanese Unexamined Patent Application Pub. No. 2008-243269 is a technique which counts the number of writes to a data track and rewrites the data in the adjacent tracks when the write count reaches a threshold. This technique counts the number of writes to a plurality of tracks formed into a group, and rewrites the group and the adjacent tracks to the group when the count reaches a threshold. Thus, by counting the writes to the group, the memory region for storing the number of writes can be reduced. Furthermore, by rewriting the adjacent tracks of the group in addition to the group, read hard errors can be more reliably prevented.
In the technique disclosed in Japanese Unexamined Patent Application Pub. No. 2005-004869, thresholds are set for the values of the date of the last update of the data track, the number of updates to the adjacent data tracks, the number of reads, etc. When these values exceed the thresholds, the data tracks are rewritten. Furthermore, this reference discloses that the thresholds are changed by the temperature history, the operation history, and the error rate.
Simultaneously to the functions described above, however, the write count, which becomes the basis for rewriting the data tracks, also decreases as the data recording density increases. For example, a conventional HDD rewrites the data every 100,000 writes, but modern HDDs must rewrite the data every 50,000 writes in order to avoid degradation of the data. In addition, the number of data tracks which must be rewritten increases with the increase in the data recording density.
The data rewrites affect the HDD performance. The increase in the frequency of the starting of the above function due to the increase in the data recording density can no longer neglect the negative effect on the performance, e.g., the number of rewrites on modern HDDs is degrading their performance. Furthermore, the increase in the number of data tracks to be rewritten further increases the negative effect on the performance when performing current rewriting schemes.
Consequently, a technique is desired which can avoid the loss of data in the other data tracks caused by data writes to a data track while suppressing deterioration in the performance of the HDD.